Organic EL element and method of manufacturing the same, organic EL display device using the element, organic EL material, and surface emission device and liquid crystal display device using the material

ABSTRACT

In an organic EL element, an organic EL layer is interposed between anodes and cathodes formed on a substrate. Each of the cathodes is made of a first conductive film that comes into contact with the organic EL layer and a second conductive film that constitutes a laminated structure together with the first conductive film.  
     The first conductive film contains any one of an alkaline metal and an alkaline earth metal. The second conductive film contains any one of at least one type metal selected from a group consisting of Ru (ruthenium), Rh (rhodium), Ir (iridium), Os (osmium) and Re (rhenium) and its oxide.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an organic EL(Electroluminescence) element having a structure in which an organic ELlayer is put between a pair of electrodes, an organic EL display deviceemploying the element, organic EL material, and a plane emission deviceand a display device employing the material.

[0003] 2. Description of the Prior Art

[0004] In recent years, the organic EL element (the organic LED) is wellappreciated as the spontaneous emission element. The organic EL elementhas the advantage that such element can be driven by the low voltagerather than the inorganic EL element and also the advantage that suchelement can be manufactured without complicated manufacturing processesin contrast to the inorganic LED in the prior art.

[0005] Also, in comparison with the liquid crystal display device thatis widely used at present as the display of the mobile device, theorganic EL element has a quick response speed, has a simple devicestructure, and needs no back-light. Therefore, the organic EL elementhas the advantage that such element can be reduced in weight. Inaddition, since the organic EL element is the solid state element, suchelement has the merit that it is resistant to the impact.

[0006] The organic EL element has the structure that the EL emissionlayer (the organic EL layer) is put between the cathode and the anode.The metal having the large work function is employed as the anode andthe metal having the small work function is employed as the cathode, sothat supplies of the hole and the electron can be made smooth. Normally,ITO (Indium-Tin Oxide) as the transparent conductor is employed as theanode.

[0007] Also, the metal containing the alkaline metal or the alkalineearth metal such as Na (sodium), Na-K (sodium-potassium) alloy, Mg(magnesium), Li (lithium), Mg/Cu (magnesium/copper) mixture, In(indium), etc. is employed as the cathode.

[0008] Alq₃, BeBq₃, DCM, DPVBi, quinacridone derivative, coumalin, etc.,for example, is employed as the EL emission layer. Normally, the monomerEL emission layer is formed by the vacuum evaporation method, and thepolymer EL emission layer is formed by the spin coating method.Accordingly, the polymer EL emission layer has the advantage that thefilm formation is easy and also the mechanical strength is high.

[0009] In addition, in order to lower the operating threshold voltage ofthe organic EL element, the trial for forming the buffer layer on thecathode side or the anode side is made. For example, sometimes the layermade of ruthenium oxide (referred to as “RuO” hereinafter), molybdenumoxide (referred to as “MoO” hereinafter), or vanadium oxide (referred toas “VO” hereinafter) is formed as the buffer layer between the anode andthe organic EL layer in the prior art. The layer made of RuO, MoO, or VOis formed by the sputter method.

[0010] By the way, if the organic EL element is used for a long time,the luminous efficiency is lowered due to the influence of the oxygenand the moisture and also the defect called the dark spot is caused.This is due to the fact that the alkaline metal or the alkaline earthmetal employed as the cathode is easily oxidized.

[0011] In Patent Application Publication (KOKAI) Hei 7-169567 as thepreceding literature, in order to avoid the degradation of the luminousefficiency of the organic EL element due to the oxygen and the moisture,it is proposed that the laminated body consisting of the anode, theorganic EL layer, and the cathode should be covered with the layerformed of material that can adsorb, occlude, or consume the oxygen(referred to as a “sealing layer” hereinafter).

[0012] Then, the material such as magnesium oxide, magnesium carbonate,iron oxide, titanium oxide, bentonite, or the like, that is impregnatedwith platinum, palladium, rhodium, ruthenium, or silver at aconcentration of less than 5 wt %, etc. are set forth as the material ofthe sealing layer.

[0013] However, the problems discussed in the following are pointed outin the organic EL element disclosed in the above literature. That is,since the laminated body consisting of the anode, the organic EL layer,and the cathode is covered with the insulating sealing layer, theleading electrode that is extended to the outside of the sealing layermust be provided to the anode and the cathode respectively. As a result,the manufacturing steps become complicated and also the rise of theproduct cost is brought about.

[0014] Also, as described above, sometimes the buffer layer made of RuO,MoO, or VO is formed by the sputter method in order to lower theoperating threshold voltage.

[0015] However, this method has the drawback that the large unevennessis formed. If it is tried to form the RuO₂ layer of 30 nm thickness bythe sputter method, for example, the hillock having a height of 50 to100 nm is locally generated. As a result, there is the possibility that,if the thickness of the organic EL layer is reduced, conversely theshort-circuit defect is caused.

[0016] In addition, in case the full-color image display device usingthe organic EL elements is fabricated, the organic EL elements for thered color emission, the organic EL elements for the green coloremission, and the organic EL elements for the blue color emission mustbe aligned in both the horizontal direction and the vertical directionin the predetermined order.

[0017] Therefore, the technology for patterning finely the organic ELlayers is requested. As the fine pattern technology used inmanufacturing the semiconductor device, the lift-off method and theetching method are well known.

[0018] However, in the case of the monochromatic image display device,it may be considered that, for example, the upper electrodes (thecathodes) of respective pixels are formed by the lift-off method. But itis difficult to apply the lift-off method to the manufacture of thefull-color image display device.

[0019] Further, since the organic EL layer is formed of the monomer orpolymer organic, such organic EL layer has the drawback that it cannotbe worked by the fine pattern technology such as the dry etching, etc.

[0020] Moreover, the above organic EL element is noted with interest asthe back-light device in place of the cold- cathode lamp that isemployed in the liquid crystal display device. The cold-cathode lamp,that is employed as the back-light device in the prior art, has the lowluminous efficiency and also occupies about 30% of the overall cost ofthe liquid crystal display device, which is a factor of the cost up.

[0021] The monomer and polymer materials are known as the organic ELmaterial. Normally the film of the monomer EL material can be formed bythe vacuum evaporation method, whereas the film of the polymer ELmaterial can be formed by the coating method. Therefore, the polymer ELmaterial is advantageous in manufacturing cost.

[0022] Since the back-light device using the polymer organic EL materialcan be driven by the low voltage, the reduction in the consumption powerof the liquid crystal display device can be expected and also the costdown and the reduction in size of the device can be expected rather thanthe cold- cathode lamp in the prior art.

[0023] However, the actual circumstances are that the organic ELmaterial that is available in practical use has not been developed yet.

SUMMARY OF THE INVENTION

[0024] Therefore, in view of the above circumstances, it is an object ofthe present invention to provide an organic EL element and a method ofmanufacturing the same, that is capable of simplifying its manufacturingsteps, lowering the product cost, and avoiding the degradation in theluminescence characteristic and the short-circuit defect of an organicEL layer due to the oxygen and the moisture not to cover a laminatedbody consisting of an anode, the organic EL layer, and a cathode with aninsulating sealing layer, and an organic EL display device employing theorganic EL element.

[0025] Also, it is another object of the present invention to provideorganic EL material available in practical use, that can be driven by alow voltage, is capable of achieving the reduction in the powerconsumption, and achieving the cost down and the reduction in size, anda plane emission device and a display device employing the material.

[0026] In order to achieve the above objects, an organic EL element ofthe present invention comprises:

[0027] an organic EL layer formed between an anode and a cathode; and

[0028] the cathode consisting of a first conductive film that contactsto the organic EL layer and a second conductive film that constitutes alaminated structure together with the first conductive film, the firstconductive film containing any one of an alkaline metal and an alkalineearth metal, and the second conductive film containing a metal that isable to prevent entering of an oxygen and a moisture into the firstconductive film when the metal is oxidized.

[0029] Also, an organic EL element manufacturing method of the presentinvention comprises the steps of:

[0030] forming an anode on a substrate;

[0031] forming an organic EL layer on the anodes;

[0032] forming a first conductive film, that contains any one of analkaline metal and an alkaline earth metal, on the organic EL layer; and

[0033] forming a second conductive film laminated on the firstconductive film and containing a metal that is able to prevent enteringof an oxygen and a moisture into the first conductive film when themetal is oxidized.

[0034] Also, an organic EL element of the present invention comprises:

[0035] an anode;

[0036] a buffer layer which is formed of at least one type metalselected from a group consisting of Ru, Mo, and V on the anode and asurface of which is oxidized;

[0037] an organic EL layer formed to be contacted to an oxidized surfaceof the buffer layer; and

[0038] a cathode formed on said organic EL layer.

[0039] Also, an organic EL element manufacturing method of the presentinvention comprises the steps of:

[0040] forming an anode on a substrate;

[0041] forming a buffer layer, which contains at least one type metalselected from a group consisting of Ru, Mo, and V, on the anode;

[0042] oxidizing a surface of the buffer layer;

[0043] forming an organic EL layer on the buffer layer; and

[0044] forming a cathode.

[0045] Also, an organic EL display device of the present inventioncomprises:

[0046] a substrate;

[0047] a lower electrode formed on the substrate;

[0048] an organic EL layer formed on the lower electrode to have areasin which a conjugate length of polymer is different each other so thatthese areas have two different luminous colors or more; and

[0049] an upper electrode formed on the organic EL layer.

[0050] Also, an organic EL display device manufacturing method of thepresent invention comprises the steps of:

[0051] forming a first electrode on a substrate;

[0052] forming an organic EL layer formed of organic EL material, inwhich a conjugate length of polymer is changed in response to lightirradiation, on the first electrode;

[0053] irradiating partially a light onto the organic EL layer to changethe conjugate length; and

[0054] forming a second electrode on the organic EL layer.

[0055] Further, in order to achieve the above objects, organic ELmaterial of the present invention consists of:

[0056] material made of organic material expressed by a general formula(1)

[0057] (Where A is a residue obtained by removing at least four hydrogenatoms from an aromatic compound or a heterocyclic compound,

[0058] X is an atomic group to which at least two groups that areselected from a group consisting of a residue obtained by removing atleast two hydrogen atoms from benzene and a residue obtained by removingat least two hydrogen atoms from cyclohexane are bonded,

[0059] Y is an atomic group to which a residue obtained by removing atleast two hydrogen atoms from benzene is bonded or at least two residueseach obtained by removing at least two hydrogen atoms from benzene arebonded, and

[0060] k, m and n are an integer respectively.)

[0061] Also, a plane emission device employing organic material of thepresent invention, comprises:

[0062] a transparent substrate;

[0063] a transparent conductive film for covering one surface of thetransparent substrate;

[0064] an alignment film formed on a surface of the transparentconductive film;

[0065] a luminous layer made of organic material expressed by a generalformula (2)

[0066] (Where A is a residue obtained by removing at least four hydrogenatoms from an aromatic compound or a heterocyclic compound,

[0067] X is an atomic group to which at least two groups that areselected from a group consisting of a residue obtained by removing atleast two hydrogen atoms from benzene and a residue obtained by removingat least two hydrogen atoms from cyclohexane are bonded,

[0068] Y is an atomic group to which a residue obtained by removing atleast two hydrogen atoms from benzene is bonded or at least two residueseach obtained by removing at least two hydrogen atoms from benzene arebonded, and

[0069] k, m and n are an integer respectively.); and

[0070] an electrode layer formed on a surface of the luminous layer.

[0071] Also, a display device employing organic material of the presentinvention, comprises:

[0072] a transparent substrate;

[0073] a transparent conductive film for covering one surface of thetransparent substrate;

[0074] an alignment film formed on a surface of the transparentconductive film;

[0075] a luminous layer made of organic material expressed by a generalformula (3)

[0076] (Where A is a residue obtained by removing at least four hydrogenatoms from an aromatic compound or a heterocyclic compound,

[0077] X is an atomic group to which at least two groups that areselected from a group consisting of a residue obtained by removing atleast two hydrogen atoms from benzene and a residue obtained by removingat least two hydrogen atoms from cyclohexane are bonded,

[0078] Y is an atomic group to which a residue obtained by removing atleast two hydrogen atoms from benzene is bonded or at least two residueseach obtained by removing at least two hydrogen atoms from benzene arebonded, and

[0079] k, m and n are an integer respectively.);

[0080] an electrode layer formed on a surface of the luminous layer;

[0081] a liquid crystal layer arranged on a second surface on anopposite side to the first surface of the transparent substrate; and

[0082] a polarizing plate arranged on the liquid crystal layer.

[0083] According to the organic EL element and the method ofmanufacturing the same of the present invention, the cathode is composedof the first conductive film that contacts to the organic EL layer andthe second conductive film formed on the first conductive film, andentering of the oxygen and the moisture into the first conductive filmcan be prevented by oxidizing the second conductive film.

[0084] Therefore, the degradation of the luminous characteristic of theorganic EL layer and the generation of the short- circuit defect can beprevented not to cover the laminated body consisting of the anode, theorganic EL layer, and the cathode with the insulating sealing layer, andthus the generation of the dark spot can be suppressed for a long time.

[0085] Also, according to the organic EL display device manufacturingmethod of the present invention, the manufacturing steps can besimplified and thus the product cost can be lowered.

[0086] Also, according to another organic EL element of the presentinvention, the buffer layer that contains at least one type metalselected from the group consisting of Ru, Mo, and V is provided betweenthe anode and the organic EL layer, and only the side surface of thebuffer layer that contacts to the organic EL layer is oxidized by theshort-time annealing, the laser annealing, the plasma oxidation, theanodic oxidation, or the like. Therefore, the unevenness of the surfaceof the buffer layer is small, and the generation of disadvantages suchas the short circuit, etc. can be avoided if the organic EL layer isthinned.

[0087] Also, according to the organic EL display device of the presentinvention, since the areas for emitting the lights in different color bychanging the conjugate length of polymer constituting the organic ELlayer respectively are formed, the multi-color emission organic ELdisplay device can be easily manufactured.

[0088] Also, according to the organic EL material of the presentinvention, since such organic EL material contains the benzene ring inthe principal chain and contains the oxadiazole in the side chain, forexample, it can emits the polarized light.

[0089] As a result, if the organic EL material of the present inventionis employed in the back-light panel, the plane emission device that canbe driven by the low voltage and can reduce the power consumption can beobtained. Also, since the display device that is constructed by theback-light panel using the organic EL material, the liquid crystalpanel, and the polarizing plate can obtain the polarized light from theluminous layer made of the organic EL material, there is no necessitythat the polarizing plate is provided between the back-light panel andthe liquid crystal panel and thus the utilization factor of the lightcan be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

[0090]FIG. 1 is a sectional view showing an organic EL element accordingto a first embodiment of the present invention;

[0091]FIG. 2 is a plan view showing an arrangement of anodes andcathodes that constitute a display device in which organic EL elementsshown in FIG. 1 are arranged in a matrix fashion;

[0092]FIG. 3 is a plan view showing an example in which the organic ELelements shown in FIG. 1 are applied to an active-matrix organic ELdisplay device;

[0093]FIGS. 4A to 4D are views showing respective steps of manufacturingan organic EL element according to a second embodiment of the presentinvention in section;

[0094]FIGS. 5A to 5D are views showing respective steps of manufacturingan organic EL display element according to a third embodiment of thepresent invention in plan; and

[0095]FIG. 6 is a sectional view showing the pertinent portion of aliquid crystal display device that is constructed by using organic ELelements according to a fourth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0096] Embodiments of the present invention will be explained withreference to the accompanying drawings hereinafter.

First Embodiment

[0097]FIG. 1 is a sectional view showing an organic EL element accordingto a first embodiment of the present invention.

[0098] An ITO film of about 200 nm thickness is formed as an anode 12 ona glass substrate 11. Also, a poly[3-(4-alkylphenol)thiophene] film ofabout 150 nm thickness is formed as an organic EL layer (a luminouslayer) 13 in the predetermined area on the anode 12.

[0099] In addition, a laminated film having the double-layered structureconsisting of a first conductive film 14 a made of the conductorcontaining Mg and a second conductive film 14 b made of the conductorcontaining Ru is formed as a cathode 14 on the organic EL layer 13. Inthis example, a thickness of the first conductive film 14 a is about 100nm, and a thickness of the second conductive film 14 b is about 50 nm.

[0100] The anode 12 is not limited to ITO, and any conductor having thelarge work function may be employed. In this case, if the light isirradiated to the substrate 11 side, the anode 12 must be formed of theconductor that can transmit the light.

[0101] The first conductive film 14 a may be formed of the conductorcontaining the alkaline metal or the alkaline earth metal that has thesmall work function. For example, MgAg, AlLi, LiF, etc. may be employedas the material of the first conductive film 14 a. Assume that the firstconductive film 14 a is formed of MgAg.

[0102] Also, the second conductive film 14 b is not limited to theconductor containing Ru, and also may be formed of the conductor thathas the high barrier characteristic to the oxygen, more particularly,the metal or its oxide selected from the group consisting of Ru, Rh, Ir,Os and Re.

[0103] The oxides of Ru, Rh, Ir, Os and Re have also the conductivity.Accordingly, the conductivity of the cathode 14 is never damaged by theoxidation.

[0104] In addition, a TiN film or a laminated film consisting of TiN andTi (referred to as a “TiN/Ti film” hereinafter) may be employed as thesecond conductive film 14b. These films have also the good barriercharacteristic to the oxygen, and can prevent the oxidation of the firstconductive film 14 a. Also, the conductivity of both the TiN film andthe TiN/Ti film is in no way degraded even if they are exposed to theoxygen-containing atmosphere for a long time.

[0105] Further, a laminated film consisting of the conductive film, theconductive film containing the metal selected from the group consistingof Ru, Rh, Ir, Os and Re or its oxide, and the TiN film or the TiN/Tifilm may be employed as the second conductive film 14 b.

[0106] In the organic EL element constructed in this manner according tothe first embodiment, if the positive voltage is applied to the anode 12and the negative voltage is applied to the cathode 14, the organic ELlayer can emit the light.

[0107] In the first embodiment, since the second conductive film 14 bcontaining Ru is formed on the first conductive film 14 a that containsMg as the alkaline metal, Ru in the second conductive film 14 b isoxidized to prevent the entering of the oxygen into the first conductivefilm 14 a even if the organic EL element is exposed to the atmospherecontaining the oxygen or the moisture for a long time. Accordingly, theoxidation in the first conductive film 14 a can be avoided.

[0108] As a result, in the organic EL element according to the firstembodiment, the degradation of the luminescence characteristic due tothe oxygen or the moisture can be avoided and also the generation of thedark spot can be suppressed. Also, since the oxidation of the firstconductive film 14 a can be avoided, the peeling-off between the organicEL layer 13 and the first conductive film 14 a can be prevented. Inaddition, there is no necessity that the laminated body consisting ofthe anode 12, the organic EL layer 13, and the cathode 14 should becovered with the insulating material, and thus the manufacture of theelement can be facilitated.

[0109] A method of manufacturing the organic EL element according to thefirst embodiment will be explained hereunder.

[0110] First, the ITO film of about 200 nm thickness is formed on theoverall upper surface of the glass substrate 11 by the sputter method.Then, the poly[3-(4-alkylphenyl) thiophene] film of 150 nm thickness isformed on the overall upper surface of the glass substrate 11 by thespin coating method, and is used as the organic EL layer 13.

[0111] In the first embodiment, the material of the organic EL layer 13is not limited to the above poly[3-(4-alkylphenyl)thiophene. Variousorganic EL emission materials of the monomer series or the polymerseries may be employed as the organic EL layer 13.

[0112] Then, the first conductive film 14 a is formed by forming theMgAg film of about 100 nm thickness on the organic EL layer 13 by virtueof the sputter method. Then, the second conductive film 14 b is formedby forming the Ru film of about 50 nm thickness thereon.

[0113] Then, a pair of terminals that are connected to the anode 12 andthe cathode 14 respectively are formed by sputtering the metal such asAu, Al, or the like while using a metal mask. Accordingly, the organicEL element according to the first embodiment can be completed.

[0114] As shown in FIG. 2, if the anodes 12 are formed like the stripeshape and the cathodes 14 are formed like the stripe shape in thedirection that orthogonally intersects with the anodes 12, the displaydevice in which a plurality of organic EL elements (intersectingportions of the anodes 12 and the cathodes 14) 15 are arranged on theglass substrate 11 in a matrix fashion can be constructed.

[0115] In this display device, like the simple-matrix liquid crystaldisplay device, if the positive signal is supplied in sequence to aplurality of anodes 12 aligned in the vertical direction at a timing insynchronism with the horizontal synchronizing signal and also thenegative signal is supplied in sequence to a plurality of cathodes 14aligned in the horizontal direction within one horizontalsynchronization period, desired images can be displayed on the organicEL display device.

[0116] Also, the present invention can be applied to the active-matrixorganic EL display device shown in FIG. 3. More particularly, if thecathode 14 is formed every pixel and also the voltage applied to thecathodes 14 via switching elements 19, each being connected to a dataline 16, a power supplying line 17, and a scanning line 18, iscontrolled every pixel, the desired images can be displayed on theorganic EL display device. In this case, since the anode 12 is used asthe common electrode for respective pixels, there is no necessity of thepatterning.

[0117] In addition, in the above first embodiment, the case is explainedwhere the organic EL layer 13 is directly formed on the anode 12 and thecathode 14 is directly formed on the organic EL layer 13. The bufferlayer may be provided between the anode 12 and the organic EL layer 13or between the organic EL layer 13 and the cathode 14.

Second Embodiment

[0118]FIGS. 4A to 4D are sectional views showing a method ofmanufacturing an organic EL element according to a second embodiment ofthe present invention.

[0119] The second embodiment shows an example of the organic EL elementin which the buffer layer is provided between the anode and the organicEL layer.

[0120] First, as shown in FIG. 4A, the ITO film of 200 nm thickness isformed on an upper side of a glass substrate 21 by the sputter method toconstruct an anode (lower electrode) 22.

[0121] Then, as shown in FIG. 4B, the Ru (ruthenium) film of 30 nmthickness is formed on the anode 22 by the sputter method to construct abuffer layer 23. Then, as shown in FIG. 4C, the short-time annealing(RTA) is carried out at the temperature of 700° C. for 3 to 5 seconds byusing the RTA (Rapid Thermal Annealing) equipment that heats by thelamp.

[0122] The Ru on the surface of the buffer layer 23 is oxidized by thisshort-time annealing. In this case, since RuO can be generated in a veryshort time, the particle size of the RuO is small and thus the situationthat the large unevenness is formed on the surface of the buffer layer23 can be avoided.

[0123] In this case, it is preferable that a thickness of the bufferlayer 23 (the thickness before RTA) should be set smaller than 50 nm.This is because, if the thickness of the buffer layer 23 exceeds 50 nm,the light generated from an organic EL layer 24 is absorbed by thebuffer layer 23 and thus the apparent luminescence intensity is lowered.Also, Mo or V as well as above Ru may be employed as the material of thebuffer layer 23.

[0124] Then, as shown in FIG. 4D, the poly[3-(4-alkylphenyl) thiophenefilm of about 150 nm thickness is formed on the buffer layer 23 by thespin coating method to construct the organic EL layer 24. The materialof the organic EL layer 24 is not limited to the abovepoly[3-(4-alkylphenyl) thiophene, and various organic EL materials ofthe monomer series or the polymer series may be employed.

[0125] Then, the AlLi film of about 20 nm thickness is formed on theorganic EL layer 24 by the sputter method to construct a cathode (upperelectrode) 25. Accordingly, the organic EL element according to thesecond embodiment can be completed. In this case, the material of thecathode 25 is not limited to the above AlLi, and the conductorcontaining the alkaline metal or the alkaline earth metal may beemployed. Also, as described in the first embodiment, the cathode 25 maybe formed to have the double-layered structure.

[0126] Actually measured results of the operating threshold voltage andthe surface unevenness of the buffer layer after the above organic ELelement is actually manufactured will be explained hereunder.

[0127] TDP/Alq₃ is employed as the material of the EL emission layer 24and then the organic EL element is formed by the above methods, and thenthe operating threshold voltage is measured. As a result, an emissionstarting voltage is 7 V if no buffer layer 23 is provided whereas theemission starting voltage is 3.5 V if the buffer layer 23 is provided bythe above method, whereby the reduction in the threshold voltage can beconfirmed.

[0128] Also, when the unevenness of the surface of the buffer layer 23is measured, such unevenness is 5 nm to 10 nm in the second embodiment.In contrast, in case RuO₂ is formed as the buffer layer by thesputtering, the unevenness of the surface of the buffer layer is 50 nmto 100 nm. As a result, the validity of the second embodiment can bechecked.

[0129] According to the second embodiment, RuO, MoO, or VO that iseffective to lower the operating threshold voltage is formed by formingthe metal film of Ru, Mo, or V as the buffer layer 23 and then oxidizingthe surface of the buffer layer 23 by the RTA. In this case, since thesurface of the buffer layer 23 is oxidized in a short time, thesituation that the large unevenness is formed on the surface of thebuffer layer 23 can be avoided.

[0130] As a consequence, the short-circuit between the anode 22 and thecathode 25 can be avoided even if the thickness of the organic EL layer24 is reduced, and thus the organic EL element having the low operatingthreshold voltage can be fabricated.

[0131] The second embodiment can be applied to the simple-matrix organicEL display device and the active-matrix organic EL display device, likethe first embodiment.

[0132] In the second embodiment, the surface of the buffer layer 23 isoxidized by the RTA equipment that uses the lamp to heat. The surface ofthe buffer layer 23 may be oxidized by the laser beam irradiation, theplasma oxidation method, or the anodic oxidation method.

[0133] In case the surface of the buffer layer 23 is oxidized by thelaser beam irradiation, the XeCl excimer laser is employed, for example.The surface of the buffer layer 23 is oxidized in a short time byscanning the laser beam, that is shaped into the rectangular shapehaving a narrow width, in the width direction. The energy of the laserbeam is set to 390 mJ/cm₂, for example.

[0134] In case the surface of the buffer layer 23 is oxidized by theplasma oxidation method, such surface of the buffer layer 23 is exposedto the plasma containing the oxygen to oxidize the surface of the bufferlayer 23. For example, the plasma oxidation process is performed by theRF O₂ plasma method under the conditions that the processing time is 10minutes, the pressure is 40 Pa, and the power is 200 W.

[0135] In case the surface of the buffer layer 23 is oxidized by theanodic oxidation method, the mixed solution consisting of tartaric acid,ethylene glycol, and ammonia solution is employed as the electrolysissolution and the Pt (platinum) electrode is employed as the anode, forexample. Then, the surface of the buffer layer 23 is anodic-oxidized bysupplying a constant current of 5 mA to deposit a RuO₂ film.

[0136] The similar advantages such as the reduction in the operatingthreshold voltage, the avoidance of the formation of the uneven surfaceof the buffer layer, etc. can be achieved even when the surface of thebuffer layer 23 is oxidized by any one of above methods.

Third Embodiment

[0137]FIGS. 5A to 5D are plan views showing manufacturing steps of anorganic EL display device according to a third embodiment of the presentinvention.

[0138] This third embodiment shows an example of a method ofmanufacturing the full-color organic EL display device.

[0139] First, as shown in FIG. 5A, an ITO film of about 200 nm thicknessis formed by sputtering ITO on the overall upper surface of a glasssubstrate 31. Then, anodes (lower electrodes) 32 are formed bypatterning the ITO film into a stripe shape by virtue of thephotolithography. In this case, a width of the anode 32 is set to 20 μm,for example.

[0140] Then, an EL emission layer 33 is formed by formingpoly[3-(4-alkylphenyl)thiophene] on the overall display area of theglass substrate 31 by virtue of the spin coating method to have athickness of 1500 Å.

[0141] In the present invention, the material of the EL emission layer33 is not limited to poly[3-(4-alkylphenyl) thiophene]. But such ELemission layer 33 must be formed of the polymer whose conjugate lengthcan be changed by the light irradiation.

[0142] Then, as shown in FIG. 5B, the ArF laser beam is irradiated ontoareas other than the red-color pixel area (R) (i.e., the green-colorpixel area (G) and the blue-color pixel area (B)) under the condition of1000 mJ/cm². As a result, the EL emission layer that is not subjected tothe laser beam irradiation emits the red-color light (the wavelength ofabout 650 nm) whereas the EL emission layer that is subjected to thelaser beam irradiation emits the green-color light (the wavelength ofabout 510 nm) because the conjugate length is shortened.

[0143] In FIG. 5B, the red-color light emitting portion of the organicEL layer is denoted by 33R and the green-color light emitting portion isdenoted by 33G.

[0144] In this case, since the relationship between the irradiationintensity of the laser beam and the emitted color of the EL emissionlayer is different depending on the material of the EL emission layer,the laser beam irradiation conditions must be changed appropriately tomeet the material.

[0145] Then, as shown in FIG. 5C, the ArF laser beam is irradiated ontothe blue-color pixel area of the EL emission layer under the conditionof 4000 mJ/cm². As a result, the EL emission layer that is subjected tothe laser beam irradiation emits the blue-color light (the wavelength ofabout 460 nm) because the conjugate length is further shortened. In FIG.5C, the blue-color light emitting portion of the organic EL layer isdenoted by 33B.

[0146] Then, as shown in FIG. 5D, cathodes (upper electrodes) 34 areformed on the EL emission layer 33 by the lift-off method. That is,photoresist is coated on the overall upper surface of the glasssubstrate, and then windows used to form the upper electrodes are openedin the resist film via exposing and developing steps. Then, AlLi issputtered on the overall upper surface of the glass substrate to have athickness of 200 nm, and then the AlLi film on the resist film isremoved together with the resist. Thus, the cathodes 34 are formed.

[0147] The material of the cathodes 34 is not limited to above AlLi. Anyconductor that contains the alkaline metal or the alkaline earth metalhaving the small work function may be employed.

[0148] In the third embodiment, as described above, the RGB-coloremitting pixels are formed by using the polymer whose conjugate lengthcan be changed by the laser beam irradiation to change the emittedcolor. In other words, since the multi-color emitting organic EL elementcan be formed not to employ the fine pattern technology such as the dryetching, etc., that requires the area separation of the organic EL layer33 pixel by pixel, the number of manufacturing steps can be reduced andthus the production cost of the device can be reduced. Thus, thefull-color EL display device having three RGB-color pixels can beimplemented.

[0149] In the third embodiment, the organic EL layer 33 is formeddirectly on the anodes (lower electrodes) 32, and then the cathodes(upper electrodes) 34 are formed directly on the organic EL layer 33. Inthis case, the buffer layer may be formed at least between the anodes 32and the organic EL layer 33 and between the organic EL layer 33 and thecathodes 34.

[0150] In the third embodiment, the manufacturing method of thesimple-matrix organic EL display device is explained. Also, the presentinvention can be applied to the manufacture of the active-matrix organicEL display device.

Fourth Embodiment

[0151] Next, organic EL material and a plane emission device and adisplay device using the same according to a fourth embodiment of thepresent invention will be explained with reference to FIG. 6 hereunder.

[0152] The organic EL material of the present invention can be expressedby a following general formula (4).

[0153] As apparent from the above general formula (4), a principal chainis constructed by the repetition unit consisting of the residue of thebenzene, from which four hydrogen atoms are removed, and the vinylenegroup. Two side chains are bonded to the benzene ring constituting theprincipal chain.

[0154] One of the side chains is the univalent ether group having thecarbon number m. Here m is an integer to satisfy the condition of5≦m≦15, and 1 is an integer to give the number of molecules of onehundred thousand to five millions.

[0155] Next, the chemical structure of the other of the side chains willbe explained hereunder.

[0156] The alkylenedioxy group having the carbon number n, thebiphenylene group, the residue of oxadiazole from which two hydrogenatoms are removed, the phenylene group, and the univalent other grouphaving the carbon number k+1 are bonded in series to the benzene ringconstituting the principal chain in this order.

[0157] This side chain portion has properties like the liquid crystal.Here n is an integer to satisfy the condition of 5≦n≦15, and k is aninteger to satisfy the condition of 5≦k≦15. If k, m, n are set toosmall, the compound expressed by the general formula (4) is difficult todissolve into the organic solvent. In contrast, if k, m, n are set toolarge, the synthesis of the compound becomes difficult.

[0158] Next, the method of synthesizing the organic EL material will beexplained hereunder.

[0159] First, the benzene derivative expressed by a following generalformula (5) is prepared.

[0160] Also, the oxadiazole derivative expressed by a following generalformula (6) is prepared.

[0161] The compound expressed by a following general formula (7) isobtained by mixing the benzene derivative expressed by the above generalformula (5) and the oxadiazole derivative expressed by the above generalformula (6) and then adding the potassium hydroxide to the resultantsolution.

[0162] Further, the polymerization reaction is caused by addingKOC(CH₃)₃ to this compound. Thus, the organic EL material expressed bythe above general formula (4) can be synthesized.

[0163] Next, a liquid crystal display device serving as the organic ELdisplay device of the present invention employing the above organic ELmaterial will be explained hereunder.

[0164] The liquid crystal display device shown in FIG. 6 in section isconstructed to include a back-light panel 1, a liquid crystal panel 70,and a polarizing plate 80.

[0165] The back-light panel 1 has a laminated structure by stacking atransparent substrate 2, a transparent electrode 3, an alignment film 4,a luminous layer 5 and an electrode 6 in this order. The transparentelectrode 3 is formed of the indium tin oxide (ITO), and its thicknessis about 200 nm. The ITO film is formed by the sputtering.

[0166] The alignment film 4 is formed of the mixture consisting of poly3, 4-ethylenedioxythiophene (PEDOT) and polystyrenesulfonate (PSS). Thealignment film 4 is formed by the spin coating method, and its thicknessis about 200 nm. The rubbing process is applied to a surface of thealignment film 4. Polyaniline, etc. may be used as the material of thealignment film.

[0167] Next, a method of forming the luminous layer 5 will be explainedhereunder.

[0168] The solution, in which the organic EL material expressed by theabove general formula (4) is dissolved in the organic solvent such astoluene, chloroform, etc., is spin-coated on the surface of thealignment film 4. After the coating, the substrate is heated to exceedthe mesomorphic temperature of the organic EL material and then iscooled down to the room temperature. When the temperature is in excessof the mesomorphic temperature, the side chain portions containingoxadiazole as the organic EL material expressed by the above generalformula (4) are aligned in parallel with the rubbing direction of thealignment film 4.

[0169] When the substrate is cooled down to the room temperature intothe solid state, this alignment state can be maintained without theinfluence of the external electric field, etc. The electrode 6 is aconductive film made of AlLi alloy having a thickness of about 300 nm.The AlLi alloy film is formed by the vacuum evaporation, etc., forexample. The liquid crystal panel 70 is the active-matrix panelemploying thin film transistors (TFTs), for example. Since the TFTliquid crystal panel has the well known structure, the outline thereofwill be explained hereunder.

[0170] Transparent pixel electrodes 74 arranged in a matrix fashion areformed on an opposing surface of a TFT side transparent substrate 71. Atransparent opposing substrate 72 is arranged in parallel with the TFTside transparent substrate 71 so as to oppose to the pixel electrodes74.

[0171] A transparent common electrode 75 is formed on an opposingsurface of the opposing substrate 72. A liquid crystal layer containingliquid crystal material is put between the TFT side transparentsubstrate 71 and the opposing substrate 72.

[0172] Although not shown in FIG. 6, an alignment film, TFTS, a blackmatrix, and others are formed. A rotating angle of a linearly polarizedlight, that propagate through a liquid crystal layer 73 in the thicknessdirection, can be controlled by applying the voltage between the pixelelectrodes 74 and the common electrode 75.

[0173] The TFT side transparent substrate 71 is adhered to thetransparent substrate 2 of the back-light panel 1. The polarizing plate80 is adhered to an outer surface of the opposing substrate 72. Ifviewed along the direction perpendicular to the substrate surface, thepolarization axis of the polarizing plate 80 intersects orthogonallywith the rubbing direction of the alignment film 4.

[0174] Next, the operational principle of the liquid crystal displaydevice shown in FIG. 6 will be explained hereunder.

[0175] When the carriers are injected into the luminous layer 5 byapplying the DC voltage to both electrodes such that the electrode 6 actas the negative electrode and the transparent electrode 3 acts as thepositive electrode, the polarized light is irradiated from the luminouslayer 5 to the liquid crystal panel 70 side. The polarization directionof the irradiated light is in parallel with the alignment direction ofthe side chains containing oxadiazole in the above general formula (4),i.e., the rubbing direction of the alignment film 4.

[0176] If the polarized direction is not rotated when the polarizedlight passes through the liquid crystal panel 70, such polarized lightdoes not pass through the polarizing plate 80 and thus the black displaystate is obtained. If the polarized direction is rotated by 90 degree,the polarized light passes through the polarizing plate 80 and thus thewhite display state is obtained. If the rotating angle is between 0degree and 90 degree, the intermediate tone display state is obtained.

[0177] In the liquid crystal display device shown in FIG. 6, thepolarized light is irradiated from the back-light panel 1. For thisreason, no polarizing plate is arranged between the back-light panel 1and the liquid crystal panel 70.

[0178] Therefore, the utilization factor of the irradiated light can beincreased. Also, both the reduction in the consumption power and thereduction in size can be achieved rather than the case where thecold-cathode lamp is employed.

[0179] In the above fourth embodiment, the biphenylene group is bondedto the carbon atom on the principal chain side of oxadiazole in theabove general formula (4). This biphenylene group may be replaced withthe atomic group to which two or more phenylene groups and two or morecyclohexylene groups are bonded in total.

[0180] A general formula (8) shown in the following shows the case wherethe biphenylene group is replaced with the atomic group to which onephenylene group and one cyclohexylene group are bonded.

[0181] A general formula (9) shown in the following shows the case wherethe biphenylene group is replaced with the atomic group to which twophenylene groups and one cyclohexylene group are bonded like a chain.

[0182] Also, in the above fourth embodiment, the case is shown where onephenylene group is bonded to the carbon atom at the top end side of theside chain of the oxadiazole in the above general formula (4). This onephenylene group may be replaced with the atomic group to which twophenylene groups or more are bonded like a chain. Also, the case isexplained where the benzene ring is contained in the principal chain ofthe organic EL material. The structure that the residue which isobtained by removing a part of hydrogen atoms from condensed polycyclichydrocarbon, heterocyclic compound, or condensed heterocyclic compoundis contained in addition to the benzene ring may be employed.

[0183] As an example of the condensed polycyclic hydrocarbon, there maybe listed naphthalene, anthracene, or the like. As an example of theheterocyclic compound, there may be listed pyrrole, thiophene, furan, orthe like. Also, as an example of the condensed heterocyclic compound,there may be listed carbazole, fluorine, or the like.

[0184] The present invention is not limited to the above embodiments,and various variations, modifications, and combinations may be applied.

What is claimed is:
 1. An organic EL element comprising: an organic ELlayer formed between an anode and a cathode; and said cathode consistingof a first conductive film that contacts to said organic EL layer and asecond conductive film that constitutes a laminated structure togetherwith said first conductive film, said first conductive film containingany one of an alkaline metal and an alkaline earth metal, and saidsecond conductive film containing a metal that is able to prevententering of an oxygen and a moisture into said first conductive filmwhen said metal is oxidized.
 2. An organic EL element according to claim1, wherein said second conductive film contains any one of at least onetype metal selected from a group consisting of Ru (ruthenium), Rh(rhodium), Ir (iridium), Os (osmium) and Re (rhenium) and its oxide. 3.An organic EL element according to claim 1, wherein said secondconductive film is formed of any one of a TiN film and a laminated filmmade of TiN and Ti.
 4. An organic EL element manufacturing methodcomprising the steps of: forming an anode on a substrate; forming anorganic EL layer on said anodes; forming a first conductive film, thatcontains any one of an alkaline metal and an alkaline earth metal, onsaid organic EL layer; and forming a second conductive film laminated onsaid first conductive film and containing a metal that is able toprevent entering of an oxygen and a moisture into said first conductivefilm when said metal is oxidized.
 5. An organic EL element manufacturingmethod according to claim 4, wherein said second conductive filmcontains any one of at least one type metal selected from a groupconsisting of Ru (ruthenium), Rh (rhodium), Ir (iridium), Os (osmium)and Re (rhenium) and its oxide.
 6. An organic EL element manufacturingmethod according to claim 4, wherein said second conductive film isformed of any one of a TiN film and a laminated film made of TiN and Ti.7. An organic EL element comprising: an anode; a buffer layer which isformed of at least one type metal selected from a group consisting ofRu, Mo, and V on said anode and a surface of which is oxidized; anorganic EL layer formed to be contacted to an oxidized surface of saidbuffer layer; and a cathode formed on said organic EL layer.
 8. Anorganic EL element according to claim 7, wherein said cathode containsany one of an alkaline metal and alkaline earth metal.
 9. An organic ELelement manufacturing method comprising the steps of: forming an anodeon a substrate; forming a buffer layer, which contains at least one typemetal selected from a group consisting of Ru, Mo, and V, on said anode;oxidizing a surface of said buffer layer; forming an organic EL layer onsaid buffer layer; and forming a cathode.
 10. An organic EL elementmanufacturing method according to claim 9, wherein said cathode containsany one of an alkaline metal and an alkaline earth metal.
 11. An organicEL display device comprising: a substrate; a lower electrode formed onsaid substrate; an organic EL layer formed on said lower electrode tohave areas in which a conjugate length of polymer is different eachother so that these areas have two different luminous colors or more;and an upper electrode formed on said organic EL layer.
 12. An organicEL display device manufacturing method comprising the steps of: forminga first electrode on a substrate; forming an organic EL layer formed oforganic EL material, in which a conjugate length of polymer is changedin response to light irradiation, on said first electrode; irradiatingpartially a light onto said organic EL layer to change said conjugatelength; and forming a second electrode on said organic EL layer. 13.Organic EL material consisting of: material made of organic materialexpressed by a general formula (1)

(Where A is a residue obtained by removing at least four hydrogen atomsfrom an aromatic compound or a heterocyclic compound, X is an atomicgroup to which at least two groups that are selected from a groupconsisting of a residue obtained by removing at least two hydrogen atomsfrom benzene and a residue obtained by removing at least two hydrogenatoms from cyclohexane are bonded, Y is an atomic group to which aresidue obtained by removing at least two hydrogen atoms from benzene isbonded or at least two residues each obtained by removing at least twohydrogen atoms from benzene are bonded, and k, m and n are an integerrespectively.)
 14. Organic EL material according to claim 13, wherein nin said general formula (1) is an integer to satisfy a condition of5≦n≦15, and k is an integer to satisfy a condition of 5≦k≦15
 15. OrganicEL material according to claim 13, wherein A in said general formula (1)is a residue that is obtained by removing four hydrogen atoms frombenzene.
 16. Organic EL material according to claim 13, wherein X insaid general formula (1) contains any atomic group in which abiphenylene group or a phenylene group and a cyclohexylene group arebonded.
 17. Organic EL material according to claim 13, wherein Y in saidgeneral formula (1) is a phenylene group.
 18. A plane emission deviceemploying organic material, comprising: a transparent substrate; atransparent conductive film for covering one surface of said transparentsubstrate; an alignment film formed on a surface of said transparentconductive film; a luminous layer made of organic material expressed bya general formula (2)

(Where A is a residue obtained by removing at least four hydrogen atomsfrom an aromatic compound or a heterocyclic compound, X is an atomicgroup to which at least two groups that are selected from a groupconsisting of a residue obtained by removing at least two hydrogen atomsfrom benzene and a residue obtained by removing at least two hydrogenatoms from cyclohexane are bonded, Y is an atomic group to which aresidue obtained by removing at least two hydrogen atoms from benzene isbonded or at least two residues each obtained by removing at least twohydrogen atoms from benzene are bonded, and k, m and n are an integerrespectively.); and an electrode layer formed on a surface of saidluminous layer.
 19. A display device employing organic material,comprising: a transparent substrate; a transparent conductive film forcovering one surface of said transparent substrate; an alignment filmformed on a surface of said transparent conductive film; a luminouslayer made of organic material expressed by a general formula (3)

(Where A is a residue obtained by removing at least four hydrogen atomsfrom an aromatic compound or a heterocyclic compound, X is an atomicgroup to which at least two groups that are selected from a groupconsisting of a residue obtained by removing at least two hydrogen atomsfrom benzene and a residue obtained by removing at least two hydrogenatoms from cyclohexane are bonded, Y is an atomic group to which aresidue obtained by removing at least two hydrogen atoms from benzene isbonded or at least two residues each obtained by removing at least twohydrogen atoms from benzene are bonded, and k, m and n are an integerrespectively.); an electrode layer formed on a surface of said luminouslayer; a liquid crystal layer arranged on a second surface on anopposite side to said first surface of said transparent substrate; and apolarizing plate arranged on said liquid crystal layer.